The present invention relates generally to pericardial modification, and more particularly to methods and systems for modifying the pericardium to adapt it for use as a pump bladder and to improve the pumping characteristics of the pericardium as a pump bladder.
A human heart includes a pair of valved muscular pumps. The right heart includes a right atrium and a right ventricle; the left heart includes a left atrium and a left ventricle. When the heart is in diastole, the left and right atria contract, forcing blood collected therein to flow to the expanding left and right ventricles, respectively. The blood collected in the ventricles is discharged in systole by contracting the muscles in the walls of the ventricles. The valves are closed between the left atrium and the left ventricle and between the right atrium and the left ventricle to prevent blood flow back to the atria. The wall muscles of the atria are relaxed to receive blood while the ventricles contract to discharge blood. At the end of systole, the wall muscles of the ventricles are relaxed, the valves between the atria and the ventricles are opened, and the wall muscles of the atria are contracted to flow blood into the ventricles, returning the heart to diastole. Some forms of heart failure are characterized by the inability of the heart to function effectively as a pump for the patient. Congestive heart failure generally refers to a condition where cardiac output has become so low that the body""s circulatory requirements are not met.
Cardiac assist devices have been proposed for assisting heart performance. For instance, U.S. Pat. Nos. 5,707,336 and 5,910,124 disclose a ventricular assist device including an inflatable bladder that can be placed in contact with the heart to compress the left ventricle. U.S. Pat. No. 5,713,954 discloses a ventricular assist device in the form of an artificial myocardium that is wrapped around the ventricles to mimic the contraction-relaxation characteristics of the natural myocardium. U.S. Pat. No. 5,273,518 discloses a cardiac cup and/or aortic balloon pump in a cardiac assist apparatus. U.S. Pat. No. 5,131,905 is directed to a shell placed around the base of the heart for augmenting cardiac contractions.
U.S. Pat. Nos. 5,385,528, 5,533,958, and 5,800,334 are directed to an intrapericardial assist device having an inflatable cuff placed around the heart. A. Bencini et al., xe2x80x9cThe xe2x80x98Pneumomassagexe2x80x99 of the Heart,xe2x80x9d Surgery, Vol. 39, No. 3 (March 1956) discloses the rhythmical insulation of gas into the pericardial cavity via a cannula inserted though a small hole in the pericardium to produce rhythmical compression of the heart in patients suffering cardiac arrest.
The present invention is generally directed to methods and systems for treating patients suffering from heart conditions characterized by the deterioration of the pumping capability of the heart. The invention modifies the pericardium to adapt it for use as a pump bladder and to improve its pumping characteristics as a pump bladder. In specific embodiments, the pericardium is partitioned to isolate a portion of the pericardial space surrounding one or more of the cardiac chambers as the pump cavity for providing cardiac assistance using the pumping system of the present invention. The pericardium may be treated by heat, chemicals, plication, and the like to cause stiffening, strengthening, tightening, reshaping, and/or shrinking of the pericardium to enhance the performance of the pericardium as a pump bladder. The present invention will find its greatest use in patients at risk of suffering xe2x80x9ccongestivexe2x80x9d heart failure, where the heart still functions, but with a significantly reduced cardiac output. The present invention will generally not find use for the emergency resuscitation of patients suffering a sudden cardiac arrest, although it could be used on those patients after they have been resuscitated by other means and methods.
In accordance with an aspect of the present invention, a method for aiding the operation of the heart includes adapting the pericardium for use as a pump bladder having a pump cavity formed by at least a portion of the pericardial space between the parietal pericardium and the visceral pericardium. The pericardium is modified under conditions to improve the pumping characteristics of the pericardium as a pump bladder.
In some embodiments, a portion of the pericardial space is isolated to form the pump cavity by attaching a portion of the parietal pericardium to a portion of the visceral pericardium. The attachment may be made by plication or bonding with an adhesive. In a specific embodiment, the attachment occurs generally along the AV groove to form a pump cavity in the portion of the pericardial space below the AV groove. The portion of the pericardial space forming the pump cavity may be sealed.
Modifying the pericardium may include treating the pericardium by stiffening, strengthening, tightening, shrinking, reshaping, or reducing the compliance or elasticity of the pericardium, or any combination thereof. The pericardium may be treated by heating the pericardium, applying a chemical to the pericardium, plicating the pericardium, or any combination thereof.
Another aspect of the invention is directed to a method for assisting the operation of the heart in a patient suffering from congestive heart failure using the pericardium adapted for use as a pump bladder having a pump cavity formed by at least a portion of the pericardial space between the parietal pericardium and the visceral pericardium, and modified to improve the pumping characteristics of the pericardium as a pump bladder. The method includes inflating the pump bladder to provide a compressive pressure on the heart, and deflating the pump bladder to relieve or reduce the compressive pressure on the heart.
In some embodiments, inflating the pump bladder includes pressurizing the pump bladder with a fluid, such as saline. In a specific embodiment, the fluid may include an antibiotic. A fluid flow line may be fluidicly coupled to the pump bladder, for instance, by forming an opening in the parietal pericardium and connecting a tubular graft through the opening to the pump cavity in the pericardial space. A pump may be connected with the fluid flow line for pumping the fluid to inflate and deflate the pump bladder. In a specific embodiment, the pump, fluid flow line, and pump bladder are connected in a way to form a closed circuit. The pump may be disposed externally or implanted in the body of the patient.
Optionally, the method may include monitoring the activity of the heart, for instance, by coupling a sensing electrode to the heart to obtain electrical signals from the heart. The inflating and deflating of the pump bladder may be controlled according to the sensed activity of the heart to assist contraction and facilitate expansion of the chambers of the heart.
In some embodiments, the signals of the heart sensed by the sensing electrode may be used to synchronize pumping action of the pump with the sensed activity of the heart.
Optionally, if the activity of the heart falls outside a preset acceptable range, the method may include pacing the heart by coupling a pacing electrode to the heart to generate a preselected rhythm. In specific embodiments, the inflating and deflating of the pump bladder are synchronized with the pacing of the heart.